Process for preparing 3,3-dimethyl-2-oxobutyric acid

Abstract

The invention relates to a process for preparing 3,3-dimethyl-2-oxobutyric acid and salts thereof by oxidizing 3,3-dimethyl-2-hydroxybutyric acid with oxygen or oxygen-containing gases in a basic aqueous medium and in the presence of palladium catalysts and also of bismuth or bismuth compounds.

What is claimed is:  
     
         1 . Process for preparing 3,3-dimethyl-2-oxobutyric acid or salts thereof by oxidizing 3,3-dimethyl-2-hydroxybutyric acid with transition metal catalysis, characterized in that it is carried out in the presence of oxygen, palladium catalyst, bismuth and/or bismuth compounds and base.  
     
     
         2 . Process according to  claim 1 , characterized in that the palladium catalyst used is metallic palladium or palladium applied to a support.  
     
     
         3 . Process according to  claim 1 , characterized in that the palladium catalyst is selected in molar ratio of palladium to 3,3-dimethyl-2-hydroxybutyric acid or salts thereof between 1:5 and 1:20,000.  
     
     
         4 . Process according to  claim 1 , characterized in that activated carbon is used as a support.  
     
     
         5 . Process according to  claim 1 , characterized in that bismuth is used in elemental form and/or a bismuth compound in the form of oxide, hydroxide, oxide hydrate or salt of a hydrogen acid.  
     
     
         6 . Process according to  claim 1 , characterized in that the amount of bismuth and/or bismuth compounds thereof is selected in molar ratio of bismuth and/or bismuth compound to 3,3-dimethyl-2-hydroxybutyric acid or salts thereof between 1·10 −6  to 1·10 −1 .  
     
     
         7 . Process according to  claim 1 , characterized in that the bismuth and/or the bismuth compounds are used in combination with other metals and/or semimetals or compounds thereof.  
     
     
         8 . Process according to  claim 1 , characterized in that the concentration of 3,3-dimethyl-2-hydroxybutyric acid and its reaction products in the reaction solution is 5 to 30% by weight.  
     
     
         9 . Process according to  claim 1 , characterized in that the amount of base is selected in a total of 1.1 to 8 equivalents of base per mole of 3,3-dimethyl-2-hydroxybutyric acid to be oxidized.  
     
     
         10 . Process according to  claim 1 , characterized in that the base used is an alkali metal or alkaline earth metal carbonate or hydroxide, mixture thereof or corresponding aqueous solution.  
     
     
         11 . Process according to  claim 1 , characterized in that the reaction is carried out at a pressure of 0.1 to 50 bar.  
     
     
         12 . Process according to  claim 1 , characterized in that the reaction is carried out at a temperature of 20 to 150° C.  
     
     
         13 . Process according to  claim 1 , characterized in that the reaction is carried out at a temperature in the range from 60° C. to the boiling point of the reaction mixture at a selected reaction pressure.  
     
     
         14 . Process according to  claim 1 , characterized in that the reaction is terminated at an oxygen take-up of 0.4 to 0.6 mol of oxygen/mole of 3,3-dimethyl-2-hydroxybutyric acid.  
     
     
         15 . Process according to  claim 1 , characterized in that the solution obtained which contains 3,3-dimethyl-2-oxobutyric acid predominantly in the form of its salts is used further after partial or complete neutralization of the superstoichiometric base.  
     
     
         16 . Process according to  claim 1 , characterized in that 3,3-dimethyl-2-oxobutyric acid is obtained by acidifying the solution with a mineral acid, and subsequently extracting.  
     
     
         17 . A process for preparing an agrochemicals comprising incorporating 3,3-dimethyl-2-oxobutyric acid which has been obtained by a process according to  claim 1  into the agrochemical.  
     
     
         18 . The process according to  claim 17 , characterized in that the agrochemical is metribuzin.